A multi-user database includes data organized for one or more uses by multiple people. Databases may be classified by the kind of data they contain, such as bibliographic, full-text, numeric, image, and so on. Databases may also be classified according to the database model they use to organize data and represent data relationships, such as a relational model, a hierarchical model, or a network model, for example. A database schema describes database structure in a formal language supported by a database management system (DBMS). In a relational database, for example, the schema may define tables, fields, relationships, views, indexes, packages, procedures, functions, queues, triggers, types, sequences, materialized views, synonyms, database links, directories, and other aspects of a database. Schemas are sometimes stored in a data dictionary.
Database schemas may be created, accessed, and/or modified during various utilizations of the database, or in preparation for such utilizations. During database development, for example, a schema can be used to define and organize the content, relationships, and structure of the data the database is designed to hold. During database interrogation, users access the data in a database for information retrieval and report generation, in accordance with the database's schema. During database maintenance, data is added, deleted, or updated in accordance with the database's schema. Database interrogation and database maintenance are often performed using a database application, which may be a general-purpose DBMS or a special-purpose application. During application development, the schema supports development of data entry screens, queries, forms, reports, tables, and labels, for example.